Dinâmica de raízes finas em uma floresta da Amazônia Central: interações com a profundidade do solo, clima e produção de serapilheira

Abstract

Fine roots (< 2 mm diameter) have a central role in biogeochemical cycles accounting for large fluxes of carbon (C) in tropical forests. Therefore, fine root dynamics and phenological patterns mediated by climate seasonality are of increasing interest in plant ecology, improving our understanding of forest responses to climate changes. In this study we provide analysis on three years of observations on fine root dynamics in different soil layers, unrevealing relationships with climatic drivers and leaf litterfall dynamics in a Central Amazonian forest. The study was conducted at the AmazonFACE experimental site located in the Cuieiras Reserve, north of Manaus, Brazil. Fine roots were measured monthly for 3 years (November 2016 – November 2019) using minirhizotron cameras in 10 tubes inserted up to 90 cm of soil depth. Roots were analyzed in three soil layers: 0-30, 30-60 and 60-90 cm of depth. Leaf litterfall was collected biweekly at the same site and period using 24 50 x 50 cm litter traps (0.25 m²) installed one meter above the ground. Climatic data was both obtained from measurements at the K34 tower/LBA program and TRMM database (Tropical Rainfall Measuring Mission – NASA). Linear models and mixed effects linear models were used in different cases to determine relationships between fine roots dynamics and soil depth, seasons, climatic variables, and leaf litterfall productivity. We observed a marked seasonal pattern for root productivity and mortality, but not for root stocks. These changes were driven by variations in soil moisture availability over time, strongly affecting shallower soil layers. Rooting distribution in the soil profile was also dynamic, with differences of stock and productivity among layers varying over the years. Moreover, we observed an asynchronous seasonal pattern among productivity of fine roots and leaf litterfall, and higher plasticity of roots than litter production in response to environmental conditions changes. Our results show that, deep fine-roots account for a high proportion of forest productivity in Central Amazon, once they are also very dynamic at deeper layers. Furthermore, relationships with leaf litterfall production point to a possible shift in total plant C allocation between above and belowground compartments driven by climatic seasonal changes. Deeper understanding of phenological mechanisms in the Amazon forest could therefore improve predictions of its long-term response and resiliency to changing climate.